


DEPARTMENT OP COMMERCE 



Scientific Papers 



OP THE 



Bureau of Standards 

S. W. STRATTON. Director 



No. 272 

CORRELATION OF THE MAGNETIC AND 

MECHANICAL PROPERTIES 

OF STEEL 



BY 



CHARLES W. BURROWS, Associate Physicist 
Bureau of Standards 



IISSUED MARCH 29, 1916] 




WASHINGTON 

GOVERNMENT PRINTING OFRCE 

1916 



MotMgraeh 






■ i- ,,V.;; 






DEPARTMENT OF COMMERCE 



Scientific Papers 



OF THE 



Bureau of Standards 

S. W. STRATTON. Director 



No. 272 

CORRELATION OF THE MAGNETIC AND 

MECHANICAL PROPERTIES 

OF STEEL 



BY 

CHARLES W. BURROWS, Associate Physicist 

Bureau of Standards 



[ISSUED MARCH 29, 1916] 




WASHINGTON 

GOVERNMENT PRINTING OFFICE 

1916 



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OF THIS rOBUCATlON MAT BE PKOCTIRED FROM 

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CORRELATION OF THE MAGNETIC AND MECHANICAL 

PROPERTIES OF STEEL 



By Charles W. Burrows 



CONTENTS 

Page 

I. Purpose axd scope of paper 173 

II. Relation op the magnetic to the other characteristics of steel. . 175 

III. Magnetic BEHA^^OR of steel under the influence op mechanical 

stress 182 

1. Resiime of early work 182 

2. For stresses below the elastic limit 184 

3. For stresses greater than the elastic limit 188 

(a) Experiments of Fraichet 189 

IV. Inhomogeneities and flaws 200 

I. Inhomogeneities in steel rails 203 

V. Conclusions 207 

VI. Bibliography 209 



I. PURPOSE AND SCOPE OF PAPER 

So much work on this subject has been done during the last 
few years that the prospects are very bright that a magnetic 
examination of steel will furnish information of practical value as 
to its fitness for mechanical uses, without at the same time injuring 
or destroying the specimen imder test. 

This paper is a review of the work done in correlating the mag- 
netic and mechanical properties of steel. The International 
Association for Testing Materials has designated this as one of 
the important problems of to-day and has assigned its investi- 
gation to a special committee. A nimiber of investigators are 
actively engaged on this problem. 

Among the mechanical properties that have been studied in 
connection with the magnetic characteristics are hardness, 
toughness, elasticity, tensile strength, and resistance to repeated 
stresses. The well-known fact that not only do these various 
properties depend upon the chemical composition and the heat 

173 



174 Bulletin of the Bureau of Standards {Voi.13 

treatment, but that frequently very slight changes in the chemical 
composition or the heat treatment produce very appreciable 
effects on the magnetic and mechanical properties complicates 
the problem considerably. 

The numerical data of this paper are taken substantially as 
they were presented by the original investigators. It is not to be 
assumed that the data are of great importance as absolute values 
of the various constants in question. In very few cases have 
pure materials been available for the investigators. Frequently 
the methods of measurement are open to objection and essential 
conditions of the experiment are not recorded. For example, the 
amount of manganese in a carbon steel may be undetermined and 
the heat treatment uncertain, although their influence is com- 
parable in magnitude with that of carbon. However, as the pur- 
pose of this paper is to show that changes in conditions produce 
corresponding changes in both the magnetic and the mechanical 
properties, uncertainties in the absolute values will not vitiate 
their usefulness for this purpose. 

There are at least three phases of this subject that warrant 
consideration. Of first importance is the comparison of the mag- 
netic properties with the other physical properties of the material. 
If it can be shown that every variation in composition and method 
of preparation brings with it a corresponding variation in mag- 
netic characteristics, and, further, that variations in magnetic con- 
ditions are always accompanied by other physical variations, then 
it is obvious that the general physical characteristics may be 
defined in terms of the magnetic constants. Whether such a pro- 
cedure is feasible depends upon the fullness of our knowledge of 
the simultaneous magnetic and mechanical data and also upon the 
facility with which the necessary magnetic data are obtainable. 

A second important phase of this subject is the variation in 
magnetic behavior as the test piece is subjected to the influence 
of stress. The correlation here is so close that the strains set up 
in a stressed bar are accompanied by simultaneous variations in 
the magnetic behavior which change in character as the magnitude 
of the strain with respect to the elastic limit changes. 

Finally, mechanical inhomogeneities of whatever origin are 
mirrored by corresponding magnetic inhomogeneities. A mag- 
netic test may therefore be of assistance in detecting flaws in 
material where the vital characteristic is reliability. 



Burrows] Magnetic and Mechanical Properties of Steel 



175 



II. RELATION OF THE MAGNETIC TO THE OTHER CHARAC- 
TERISTICS OF STEEL 

A number of experiments have been made which show a rather 
close connection between the magnetic characteristics and the 
chemical constitution. The following four curves are taken from 
the data of Gumlich '} 




Fig. I. — Showing the variation of permeability 
with induction for steels of different carbon 
content 

Fig. I shows how the permeability varies throughout the course 
of the magnetization ciu^e for different carbon content. This 
and other experimental work indicate that for a complete series 
of iron-carbon alloys, with no other differences than their carbon 
content, the carbon content is indicated by the permeability curve. 

' Gumlich, "Magnetic properties of iron-carbon and iron-silicon alloys," Faraday Society Transactions, 
85 pp. 98-114; 1912, 



176 



Bulletin of the Bureau of Standards 



[Vol. 13 



Fig. 2 shows the connection between the saturation values of 
magnetic induction (that is, the maximum values of B-H) and 
the carbon content. Pure iron has the highest saturation value 
for the series. An addition of carbon causes a decrease in the 
magnetization at a rate almost proportional to the amount of 
carbon added. This simple relation between the saturation value 
and the carbon content holds for any particular heat treatment. 
For different heat treatments, however, the saturation value 
changes with the carbon content at different rates. A comparison 




Fig. 2 . — Showing the magnetic saturation values 
of steels of different carbon contention the an- 
nealed and in the quenched conditions 

of the two curves shows that the reduction due to the presence of 
carbon is less for the annealed than for the quenched. 

Fig. 3 shows the influence of carbon on the coerci\-e force. 
Annealed steel has a coercive force which increases linearly with 
increase in carbon until an approximately eutectic alloy is reached. 

For higher carbon contents the coercive force still increases 
linearly but at a decreased rate. Steel quenched at 800° C. shows 
a linear increase in coercive force for the hypoeutectic allo}"s and 
constant coercive force for the hypereutectics. Quenching at 
higher temperatures results in more complex relations. 



Burrows] Magnetic and Mechanical Properties of Steel 



177 



Other elements than carbon will reduce the saturation value. 
Fig. 4 shows the rate of reduction of the saturation value for 
various additions of silicon. Here also the relation between the 
reduction in the saturation value and the percentage of alloyed 
element is nearly linear. 

Waggoner^ shows that magnetic hysteresis and the maximum 
strength of steels vary in the same way with changing carbon 




Fig. 3. — Showing the variation of coercive force 
with carbon content for different heat treatments 

content. The characteristic curves of magnetic and elastic 
hysteresis show a marked similarity of shape. A comparison of 
the curve showing the relation of elongation under stress (or 
ductility) to the carbon content with the corresponding curve of 
magnetization and carbon content shows a striking similarity, 
indicating that the ductility of these alloys and their intensity of 
magnetization are affected in the same way by the chemical com- 

2 Waggoner, " A relation between the magnetic and the elastic properties of a series of unhardened iron- 
carbon alloys," Phys. Rev., 35, pp. 58-63; 1912. 



178 



Bulletin of the Bureau of Standards 



[Vol 13 



position. The maximum susceptibility -carbon ciurve is also similar 
to the curve of ductility-carbon — ^that is, the maximum suscep- 
tibility decreases with increasing carbon until the eutectic is 
reached and then again increases with increase in carbon content. 
Mars ^ shows that for a series of iron-carbon alloys there is a 
definite relation between the Brinell hardness and the residual 
induction as shown in Fig. 5. 



toeop 








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tsooo z 


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Fig. •4. — Showing the variation of the magnetic 
saturation valiie with percentage of silicon in 
iron-silicon alloys 

Goerens * has shown the changes which the magnetic charac- 
teristics of a cold- worked steel undergo after various annealings. 
This steel was cold-drawn in five steps from an initial diameter 
of 7 mm to a final diameter of 2.7 mm. Fig. 6 shows the varia- 
tion of the magnetic constants after annealing at various tem- 
peratures. Fig. 7 shows the corresponding mechanical character- 
istics. The mechanical properties are decidedly different for 
annealings below and above 500°. The same is true for the curve 
of maximum permeability. The curve of residual induction shows 

'Mars, Stahl und Eisen, 29, pp. 1673-1678; 1909. * Goerens, Stahl and Eisen, 34, pp. 282-285; i9'4- 



Burrows] 



Magnetic and Mechanical Properties of Steel 
MO 
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^ .b .8 /.O /.2 M /.(, 

Carbo/7 % 

Fig. 5. — Showing how the mechanical hardness and 
the residual induction vary with carbon content 




40000^ 

30000 s^ 



20O0O 



200 ^00 600 goo loao 

Fig. 6. — Showing the effect of the annealing tem- 
perature on the magnetic properties of a mechan- 
ically hardened steel 



23760°— 16- 



i8o 



Bulletin of the Bureau of Standards 



[Vol. 13 



a sharp maximum at 500°. The curves for coercive force and hys- 
teresis show steady decreases with increase of annealing tempera- 
ture. In general, the magnetic characteristics respond to the an- 
nealing process in just as definite a manner as do the mechanical 



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zoo ^00 bOO S:00 /OOO 

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Fig. 7. — Showing the effect of the annealing tem- 
perature on the mechanical properties of a me- 
chanically hardened steel 

properties. In fact, it would be easier to deduce the heat treat- 
ment from the magnetic data than from the mechanical. 

Fig. 8 may be considered as typical of the magnetic behavior of 
many alloy steels. The usual effect of quenching is to lower the 
induction curve. Subsequent drawing raises the curve again. 



Burrows] Magnetic and Mechanical Properties of Steel 



i8i 



This improvement in the permeability increases with increase in 
drawing temperature up to a certain maximum when the curve 
occupies approximately the position of curve C. Higher draw- 
ing temperatures cause a reduction in the permeability and the 
curve approaches approximately the position of the annealed 
material. 

Each curve corresponds to a given heat treatment and also to 
rather definite mechanical properties. The material of curve B is 



/fes/e/tfo/ 
//'/So 




-- ' . _ A/ao/ref/i/ha force 

Coerc/ve /orces 

\. — Characteristic induction curves of an alloy steel 



Fig. 8. 



so brittle that it is not usable, while that of curve A has a large 
angle of cold bend, but does not possess sufficient strength. The 
material of curve C has an ultimate strength several times that of 
curve A, accompanied by a fair degree of toughness. Not only 
do the normal induction curves show the characteristic effects of 
heat treatment, but also the residual inductions and the coercive 
forces after a magnetizing force of 150 gausses show such effects. 
It is possible to obtain a quenched and drawn steel whose induc- 
tion curve approaches closely the position of the annealed curve. 



l82 



Bulletin of the Bureau of Standards 



Vol. 13 



However, two such steels would be at once differentiated by their 
differences in residual induction and coercive force. 

Fig. 9 shows a set of characteristic curves for a spring steel of 
approximately i per cent carbon. Here, as in the case of the 
alloy steel, a high ultimate strength, coupled with a fair degree of 
toughness, is characteristic of those curves of Figs. 8 and 9 which 
are steep and of relatively high permeability. 




Fig. 9. — Characteristic curves of a carbon steel 

Fig. 10 shows the magnetic characteristics of a low-carbon steel 
after various forms of heat and mechanical treatment. The simi- 
larity between the hardening effects of cold working and of quench- 
ing is shown by the similarity of the magnetic curves. 

III. MAGNETIC BEHAVIOR OF STEEL UNDER THE INFLU- 
ENCE OF MECHANICAL STRESS 

1. RESUME OF EARLY WORK 

Matteuci in 1847 noticed that the magnetization of a permanent 
magnet was increased when the bar was subjected to tension. 

Viliari showed in 1868 that the permeability of a bar of steel 
was altered when the specimen was subjected to tension. For 



Burrows] Magnetic and Mechanical Properties of Steel 



183 



low inductions this change is an increase in permeabiHty, while 
for high inductions it is a decrease. The value of the induction 
at which tension does not alter the permeability is the "Villari 
reversal points" The permeability is modified by tension whether 
the tension is applied first and then the magnetizing force or vice 
versa. The effect is noticeable even after the tension has been 
applied and removed before the magnetizing force is applied. 
The effects of tension in these three cases differ in magnitude 



/SffOi 



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Fig. 10.— Normal induction of a low carhon 
steel under different conditions 

rather than in nature. The effect is present whether a constant 
tension is applied while the magnetizing force is varied or a vary- 
ing tension is applied to a specimen under a constant magnetiz- 
ing force. 

There is a certain value of the tension for which the induction 
is a maximum for a given field. The tension at which the indue"- 
tion is a maximum for a given field decreases with increase in 
field. In very strong fields this maximum may even disappear, 
so that the effect of any tension is to diminish the induction. On 



i84 



Bulletin of the Bureau of Standards 



[Vol. 13 



the other hand, in very weak fields the induction may increase 
with increase in tension for all stresses within the elastic limit. 

All these effects are complicated by the phenomena of hysteresis 
and the initial changes are different from those thbt occur after 
the cycle of changes has been passed through several times. 

J. J. Thomson, by a course of dynamical reasoning, has shown 
that there is a reciprocal relation between the changes in dimen- 
sions produced on magnetization and the changes in magnetiza- 
tion produced by mechanical strain. From this theoretical con- 




FlG. II 



sideration it is possible to foretell one set of phenomena from the 
data on the other. Both sets of phenomena have been carefully 
investigated and the reciprocal relation verified experimentally. 



2. FOR STRESSES BELOW THE ELASTIC LIMIT 

Figs. II to 1 6 are taken from an article by Smith and Sher- 
man ^ and illustrate in detail the magnetic changes due to tension 
and compression. 

» Smith and Sherman, Phys. Rev., N. S., 4, pp. 267-273; 1914. 



Burrows] Magnetic and Mechanical Properties of Steel 



185 



In this investigation the materials studied were rail steel, mild 
steel, and silicon steel such as used in transformer plate. Test 
samples 60 cm long and i cm in diameter were subjected to 
various tensions and compressions and the magnetic induction 
curves simultaneously determined by the Burrows method. 

If a low magnetizing force is applied to a rod under compression 
with a successively decreasing load, the permeability gradually 
increases with a steady decrease in this rate of increase as zero 
load is approached. If tension is applied, the permeability still 



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20 



30 




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2S0O /U 
/SOO /U 



40 



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Fig. 12 

increases at a diminishing rate until a certain value of load is 
reached at which the increase ceases. For larger loads the per- 
meability becomes smaller as more tension is applied. The change 
in rate seems nearly constant and in the same direction throughout. 
In all the samples the Villari reversal was found for tension, but 
not in all cases for compression, although the form of the curve 
indicated that at higher inductions the reversal might be expected 
for compression also. The effect of compression was to decrease 
the permeability at low values of H and to increase it at high 



1 86 



Bulletin of the Bureau of Standards 



{Vol. 13 



values of H, but in much greater degree than the corresponding 
changes due to tension. The stresses ranged from a tension of 
2500 kg per square centimeter to a compression of 1000 kg per 
square centimeter. 

Magnetizing forces from 30 to 55 gausses were used. The great- 
est change in permeability was found in wrought iron, which showed 
at a magnetizing force of 15 a decrease from 14 200 gausses to 
8600 gausses under a compression of 1000 kg per square centi- 
meter. 




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III 



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30 



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500 he 

1000 Hi 



60 



Fig. 13 

The complicated manner in which the magnetic induction varies 
with the tension for different magnetizing forces is brought out 
in Figs. 17, 18, and 19.® Fig. 1 7 shows that for moderate values 
of the magnetizing force the induction is always increased by the 
application of a small tensile load and decreased by a large load. 
The intermediate load, which produces a maximum induction for 
the corresponding magnetizing force, is greatest for low magnetiz- 

' Figs. 17-19, 22-25, and 27 are takaa, with some modification, from the thesis of Paul D. Merica, " Ueber 
BeEiehungen zwischen den mechanischen imd den magnetischen Eigenschaften einigen Metalle bei elas- 
tiscben und plastischen Ponnandenmgen," Diss. Berlin; 1914. 



Burrows] Magnetic and Mechanical Properties of Steel 



187 



ing forces and decreases as the magnetizing force increases, as 
shown in Fig. 18. The numerical value of the maximum increase 
produced by tension varies through wide limits, as shown by Fig. 1 9. 

Fig. 20^ shows the hysteresis in the magnetic induction when 
the tension is varied in a cyclic manner. It also shows the dif- 
ference between the variation of magnetic induction when the 
load is first applied and that which occurs in succeeding cycles. 

Fig. 21 presents in a slightly different form this same magnetic 
hysteresis after a change in tension. The magnetic effect of any 
mechanical stress depends not only upon the existing stress but 
also upon the previous stresses which have been impressed upon 
the specimen. "Work done by the author tends to show that this 
aftereffect of a given load is reduced, if not completely obliter- 



3 



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30 




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'^ht Jo. 



un ier Ter j/'on 



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SO 



Fig. 14 

ated, with the lapse of time. Merica shows that if the elastic limit 
has not been passed the magnetic effect of any stress may be 
wiped out by demagnetization. 

In the experiment, the results of which are shown in Fig. 22, 
the test piece was strained beyond the elastic limit. At several 
stages the load was held constant while the bar was demagnetized 
and its induction determined. The hysteresis in both the mag- 
netic and mechanical properties is worthy of note. For stresses 
within the elastic limit neither mechanical nor magnetic curve 
shows any hysteresis. We must not confuse the procedtire of this 
experiment with that of Fig. 20, in which the magnetizing force 
was applied continuously without intermediate demagnetization. 

' Figs. 20, 21, and 26 are taken, with some modification, from Ewing, " JIagnetic induction in iron and 
other metals." 

23760 °~16 3 



1 88 Bulletin of the Bureau of Standards [Voi.ij 

3. FOR STRESSES GREATER THAN THE ELASTIC LIMIT 

The magnetic behavior of a bar under tension is altered by 
stressing beyond the elastic limit. The influence of stretching is 
shown in Fig. 23, where it is evident that both the contour and mag- 
nitudes of the curves are changed. Fig. 24 shows how the tension 
required to give the maximum induction for a given magnetizing 
fqrce varies with the elastic limits which have resulted from pre- 
vious stretching. The curve for the upper magnetizing force is 
so nearly a straight line that it is possible to determine intermedi- 
ate elastic limits from the magnetic data. 



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Fig. is 

Fig. 25 shows the manner in which the magnetic flux decreases 
during the elongation of the bar. The decrease in flux is not pro- 
portional to the elongation, so that it is evident that there is some 
change other than a decrease in cross section taking place within 
the bar. It is further evident that the greater part of this struc- 
tural change takes place during the initial elongations. 

The magnetic properties of all magnetic materials are modified 
under tension, though not all in the same manner. Nickel, for 



Burrows] Magnetic and Mechanical Properties of Steel 



189 



instance, shows an increased magnetic induction under compres- 
sion and a decreased induction under tension, while iron shows 
the reverse. Fig. 26 gives some idea of the magnitude of these 
magnetic changes in nickel. 

Fig. 27 shows the variation in induction with increase of tension 
for a sample of nickel steel. The change in induction as the 
tension reaches the elastic limit is very marked, both in the 
annealed and the stretched condition. 




Fig. 16 



A general view of the effect that tension below the elastic limit 
will have on a given material is obtained by a consideration of 
the curves of magnetostriction,^ Fig. 28. If a material shoAvs 
elongation for a given field, it also shows increased induction 
under tension, and vice versa, for the same field. 

(a) Experiments of Fraichet.^ — Method. — ^The bar imder test 
is placed in a tensile testing machine and the jaws sepa- 
rated at a constant velocity. A solenoid which smrounds 

' S. R. Williams, Phys. Rev., 34, p. 44; 1912. 

' L. Fraichet, "Nouvelle methode d' essai des m^taux magnctiques," Eel. Elc, 30, pp. 361-369 and 
413-422; 1903. 



igo 



Bulletin of the Bureau of Standards 



[Vol. IS 



the test bar carries the magnetizing current. A small test coil 
also surrounding the test specimen is connected to a suitable 
galvanometer. This test coil is linked with the flux in the bar 
under tension and any change in this flux gives rise to a correspond- 
ing emf which is indicated by the deflection of the galvanometer. 



tOOOOi 



nsoo 



isooo 



tssoo 



/oooo 




'7SO0 



g-QOO 



ZSOO 



I Fig. 17. — Showing the effect of tension on the mag- 

'■ netization under different field strengths 

Causes of flux variation. — The flux may vary from any or all of 
three causes: (i) The reluctance of the joints and parts of the 
magnetic circuit other than the specimen may change; such 
variations occur when the tension is first applied but die out as 
soon as the grips of the machine make good contact with the 
specimen', (2) the reluctance will decrease as the continued ap- 



Burrows] Magnetic and Mechanical Properties of Steel 



191 



to 



/o 



t 







7000- 



SOOO 



/o so 30 ^o so *o 



Fig. 18. — Showing the tension required to pro- 
duce the maximum induction for a given field 



7S00 



saoo 



ZSoo 




Fig. 19. — Showing the maximum 
increase in induction which can 
be produced by tension 




3000 



/mm* 

Fig. 20. — Showing the changes in mag- 
netic induction due to the loading and 
unloading of a bar under a constant 
magnetizing force 



19^ 



Bulletin of the Bureau of Standards 



[Vol. 13 



plication of tension causes the bar to decrease in cross section; 
(3) changes in the molecular structure of the metal due to the 
cold working will probably cause changes in reluctance. Changes 




Fig. 21. — Showing the effect on the magiietic mduction due to 
loads which have been applied and removed before the magnet- 
izing force is applied 



6S0C 




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=x 




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1 




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I 


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Fig. 22 . — Showing hysteresis in the inagnetic and the 
mechanical properties of a steel under a chatiging 
ter-sile force whose -maximum exceeds the elastic 
limit 

in the cross section will be manifested by gradual changes in 
reluctance, while changes in the structure will take place more 
or less suddenly. 



Burrows] Magnetic and Mechanical Properties of Steel 



193 



In Fig. 29 the variation of magnetic flux is plotted against the 
time since the tension machine was started. Ctnve //, which 
may be taken as a typical curve of this type, shows several well- 
defined regions. The initial deflection of the galvanometer is 
positive and may be accomited for by improvement in joint 
contacts and the well-known increase in permeability due to 



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££■00 



Fig. 23. — Showing now the effect of tension on the 
magnetic properties is modified by cold working 

tension. This region is of no particular importance in the present 
series of experiments and may exhibit many apparent irreg- 
ularities. The second region is one indicating a decreasing flux 
and ends with the point of maximum rate of decrease. This 
point corresponds to the limit of proportionality between stress 
and strain. This is the true elastic limit which we may define 
as the maximum load whose momentary application produces no 



194 



Bulletin of the Bureau of Standards 



[Vol. 13 



marked modification in dimensions of the bar nor in physical or 
chemical properties of the metal 

The third region is one of more or less violent vibrations of the 
galvanometer. These magnetic disturbances begin at the yield 
point of the metal, which is spoken of as the "apparent elastic 
limit." The fourth, or plastic region, is one of gradual decreasing 
galvanometer deflections terminated by a sudden but slight drop 
at the commencement of stricture. The last region shows a 
rapidly increasing reluctance, and terminates at rupture. 




FzG. 24. — Showing how the elastic limit of a series of 
cold-worked steels varies with the stress required to 
give maximum induction for a given field 

The other curves of Fig. 29 show that the nature of these main 
characteristics is not altered by the value of the magnetizing ciur- 
rent employed. Fig. 30 shows the change in tension with time. 

If in the initial bar the hardness of the volume elements varies 
continuously from one part of the bar to another, the molecular 
transformation of the same elements takes place in a continuous 
manner. This is what we observe in a quenched bar. The struc- 
ture of the metal varies continuously. The galvanometer deflec- 
tion at first increases, passes through a maximum corresponding 
to the true elastic limit, and finally decreases with a regularity 
dependent upon the initial homogeneity. 

If the distribution of hardness is discontinuous the molecular 
transformation of the bar will be equally discontinuous, as indi- 



Burrmes] Magnetic and Mechanical Properties of Steel 



195 



zooop 



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cated by the variations in the galvanometer deflections after the 

limit of true elasticity is reached. We observe these phenomena 

in bars of soft iron or annealed steel. 

An annealed bar is therefore composed 

of elements of varying hardness. Cold 

working reduces the number of these 

groups, and consequently produces an 

elevation of the true elastic limit. 

Quenching gives the same hardness to 

all those elements situated on the 

same concentric layer. A quenched 

bar is therefore composed of layers 

having a hardness decreasing from the 

outside inward. 

When the hardest elements have 
been transformed by the cold working, 
the flux varies only as a result of change 
in dimensions. The elements glide one 
over the other. The specific load cor- 
responding to the commencement of 
the plastic period is easily measured, 
and in the opinion of Fraichet may 
characterize completely the material. 

Cold working acts on all the elements 
of volume and renders the bar homoge- 
neous, and consequently the true elastic 
limit approaches the plastic load, which, 
in ttun, approaches the ultimate. The 
effect of cold working is shown in Fig. 3 1 



S600 

B 




% ^/o/7j ygf/p/f 



€ 



2 ^ 

Fig. 25. — Showing the decrease in 
magnetic induction correspond- 
ing to a given magnetizing 
force when the test specimen is 
stretched beyond the elastic limit 

. On the first loading we 
pass the true elastic limit below 4800 and at 4800 the metal is 




Fig. 26. — Showing how the m.agnetization curve of nickel changes 
under tension and under compression 

yielding. When the load is removed and reapplied the true elas- 
tic limit is raised to 4800 and the yield point is about 4850. Re- 



196 



Bulletin of the Bureau of Standards 



Vol. 13 



f7S0 



tsoo 




liicKe/ sStee/ 

Fig. 27. — Showing the variation of magnetic induction 
with tension for nickel steel 



»0 


/"^ei/s/ef 


A//aw 


Cs^tCo^sIl — 












— 




<o 


'^:^ 


^"^ 


^fee/ 




\-M 






•?7 


\ 




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Hj •* 


v_ 




/i/c/fe/ 




-4. 


H-' ^ 


00 1 


000 / 


Soo^ 



Fig. 28. — Magneiosiriction curves 



Burrows] Magiietic and Mechanical Properties of Steel 



197 



moving the load again and reapplying it results in a true elastic 
limit of 4850, followed immediately by the plastic yield and final 
rupture. In other words, the bar is homogeneous. 



Trt/e £.L S600 




-w 



xiecondt 




i 



U H=/0 gausses 
m H' flesic/ua/ fie/d di/e to f>rfviOi/s 
/Trag/jet/zat/on. 



Fig. 29. — Showing magnetic changes in a bar loaded to the point 

of rupture 

Fig. 32 shows characteristic magnetic curves for test bars of the 
same composition, but of different heat treatments. 

The true elastic limit is easily determined by this magnetic 
method, and corresponds to a critical point of molecular equilib- 




»/0/7 of T/ITIf 



600ff, 



fiuptorA 

Jfef/ecf/on.t as fUHi ^' 
time 



Fig. 30. — Showing the changes in tension and 
in the magnetic properties when the tensile 
machine motor is driven uniformly 

rium. The apparent elastic limit or yield point is a function of 
the previous working of the metal, and consequently does not 
characterize the metal. The nature t)f the material is best indi- 
cated by the specific plastic load. 



198 



Bulletin of the Bureau of Standards 



ivoi.13 



Fraichet ^"j elsewhere in a paper on "Sudden variations in 
reluctance of a magnetized steel bar submitted to fracttne as 
related to Luder's lines," notes the appearance of lines on the 



2"" Loac/ma 



•■^eso 




T'me 



O to Fifpture 



7//ne 



Fig. 31. — Showing how the cold working of successive loadings 
beyond the elastic limit changes the magnetic and mechanical 
properties 



£ljtrue) 

-\ esoo 



and not an 



Quenched (loo'CJ in o// 
ant/ not drawn. 

/^ax. £.oad-/29O0 
/fu/>tt/re 




/n o// 900 
'rawn 
/^ax. Load' /2 600 



Cpe/e/7cAed/n wate/^ 
one/ nofc/rawn 

/^axJ.O0d'9eoo 



Quenched /n wntfr of 9CoX 
and drown 



ySrricPon ^eg/ns 
/-fXoo. 



Fig. 32 . — Showing how the magnetic changes in a 
hat subjected to tension up to the point of rup- 
ture depend upon the previous heat treatment 

surface of a test bar of steel under a tensile force which corre- 
spond exactly with a sudden variation in the magnetic reluctance 
of the bar. It seems highly probable that the same cause gives 



' Fraichet: C. R., 138, pp. 355-356; 1904. 



Burrows] Magnetic and Mechanical Properties of Steel 



199 



rise to both these phenomena. Whenever the formation of fresh 
Hnes is observed the variation in reluctance is discontinuous, while 
no new lines are formed as long as the variation in reluctance is 
not abrupt. 







i/nc^er /.oaaf 








/£ 


X^ 






\^ 




/ 


/ 






A 

t 




8 / 












/ 


Loacf fiemouec^ 




f 


^ 














t 







-^ 


000 8 


000 







I 

o 



I 



L.oacf 
Fig. j,^. — Showing the magnetic induction under load and after the removal 

of load 

In Fig. 33 curve A shows the variations in magnetic induction 
of a bar of machinery steel under various loads in tension. The 
induction increases with initial load up to a maximum and then 




Fig. 34. — Showing the variations in induction for different parts of 
a bar during tension 

decreases. At a load which corresponds roughly to the elastic 
limit the induction decreases abruptly. Ctuve B shows the in- 
ductions obtained after the loads indicated by the abscissae have 



200 



Bulletin of the Bureau of Standards 



[Vol. 13 



been applied and removed. This curve is almost a straight line 
throughout the greater part of its length and falls off abruptly 
as the elastic limit is reached. 

Fig. 34 shows curves of induction under load in which the varia- 
tion in the induction over three sections of the bar 10 cm apart 
were determined. The break occurred over the section 95, which, 
although it had the greatest induction for initial loads, showed 
the lowest induction at loads approximately the breaking strength. 
As the material began to yield, the load was decreased slightly, 
with a corresponding rise of induction as shown. If we assume 
that initially the greater part of the material at section 95 was 
under some internal tensile strain, we have at once the explana- 
tion of the higher initial induction and the lower final induction, 
together with the rupture at this section. 

IV. INHOMOGENEITIES AND FLAWS 

When a bar of steel is placed in a magnetic field the magnitude 
of the induction and other magnetic phenomena is determined 







X 


/- 


\ 








i? 


/ ^^ 


y \ 


u 


/ / ^ 


^iy \ 


^ 


/ X— ^ "^ 


\ 


c 


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\ 


0> 


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V 


1 / € 


\ 


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Positimt along, Lfn^tk of rvJ 

Fig. 35. — Showing irregularities in distribution oj 
flux in a rod which has been rendered nonhomo- 
geneous by stamping numbers as indicated by 
the arrows 

by the nature and amount of material present. From this it 
follows that if a magnetic exploration is made along the length of 
a bar, magnetic variations may be expected in nonhomogeneous 
material. The following experiments bear this out. 

In Fig. 35" is shown the variations in magnetic induction in a 
bar which forms one side of a rectangular magnetic circuit and is 
magnetized by a surrounding solenoid. The upper curve shows 
the normal variation of flux in a bar vv'hich is approximately imi- 



■ Burrows, Bull. Bureau of Standards, 6, p. 62, 1909 (Reprint No. 117). 



Burrmvs] Mognctic and Mechanical Properties of Steel 



20I 



form. The lower curve shows the variation of flvix in the same 
bar after a single number has been stamped on the bar at each of 
the points indicated by the arrows. The magnetic changes pro- 
duced by the stampings are evidenced by a decided reduction in 
the induction at these points. 

Fig. 36^2 shows the variation in permeability along the lengths 
of each of two bars both before they have been distorted (dotted 
lines) and after they have been bent through a given angle and 
then restraightened (solid lines). After this last operation each 
bar was broken in a tensile testing machine. The permeability 
shows a remarkable change due to the bending. In the imme- 



^ 






^ 



3ro/<e 
/fere 



\J3ro/fe 
'^ /fere 



-'^^ 





3enr^S'ancl 
ySfra/^fyte/jee/ 

^ar A 



3enr (,0' and 
,i froightened 



^ar 3 



Fig. 36. — Flux distribution of a bar before and after bending and 
res traigh tening 

diate neighborhood of the bend there is a region of increased per- 
meability and close to it a region of decreased permeability. In 
each case the rod broke in the region of maximum permeability. 
In this connection we may refer back to Fig. 34, where, it was 
noted, the break occurred over the section which had initially a 
maximum permeability. 

The magnetic homogeneity of a bar may be investigated in 
terms of the flux distribution when placed in a magnetic field. 
With a single stationary coil one may measure the total flux. 
With two opposing stationary coils the magnetic leakage may be 



'2 Figs. 34 and 36 are taken from a paper by the author presented before the American Physical Society, 
April, 1912. 



202 



Bulletin of the Bureau of Standards 



[Vol. 13 



measured. With two opposing and movable test coils the varia- 
tion in leakage may be measured. Mr. Sanford, of the magnetic 
section of the Bm^eau of Standards, has perfected the details of 
this last method of examination and the author is indebted to him 
for the following curves showing certain characteristic conditions. 
In Fig. 37 are plotted the observations on seven bars which were 
originally homogeneous as shown by a preliminary examination 



C/n/for/TT 



'A 



^Saiv f^/of- 




^e/PT^ana^ /■-s.^fra/g/ife./yea/ 



C 



\ 




Fig. 37. — Mechanical inhomogeneities as shown by variations in 
the rate of change of leakage 

and were later rendered inhomogeneous in the manner indicated. 
Curve A is the record of a uniform rod and is similar to the records 
of the other rods before modification. The criterion of a uniform 
rod is an approximately straight line. An upward projection 
indicates a magnetically hard spot and a downward projection 
indicates a soft spot. The sharp upward projection of B is due to a 
saw slot 3 mm deep in a rod of 12.7 mm diameter. Rod C was bent 



Burrows] Magnetic and Mechanical Properties of Steel 



203 



through an angle of 10° and straightened, while D was repeatedly- 
compressed between the jaws of a small clamp operated by a thumb- 
screw. In each of the cases the magnetic inhomogeneity is similar 
to that caused by the saw slot. In C the bar was heated by a small 
flame and cooled in air. The resulting softness is apparent from 
the downward projection of the curve. F was heated over a 
greater length and quenched. The resultant hardness extends 
over a greater length, as might be expected. G is a bar which 
was cut in half and put together with a threaded joint and carefully 
finished surfaces, so that it presented the appearance of a contin- 
uous bar. The projection due to this treatment is striking. 



/Is /fece/'t^ecf 



^e/7t /O °ano/ /--^^STrai^h fened 

\ 



A/7nea/ecf 



Fig. 38. — Showing the effect of bending and restraightening and of 
annealing on the magnetic homogeneity along the length of a bar 

In Fig. 38 records are made of a bar as received, after bending 
and restraightening, and after annealing. It is to be noted that 
the cold bending produces a marked inhomogeneity which is 
entirely removed by subsequent annealing. 

Such tests as these which indicate the presence of mechanical 
strains, coupled with the fact that such strains may be relieved by 
heating to a temperattu-e below which structural changes occur, 
open up a wide field of possible applications. 

1. INHOMOGENEITEES IN STEEL RAILS 

At the present time the author is carrying on an investigation 
of the magnetic inhomogeneities along the length of steel rails. 

The rail to be examined and a similar rail are placed side by side. 
The rail tmder test is surrounded by a narrow test coil which is in 
electrical connection with a galvanometer. Surrounding the rail for 
some distance on each side of the test coil are two magnetizing sole- 
noids. Opposite these two solenoids and surrounding the auxiliary 



204 Bulletin of the Bureau of Standards [Voi. 13 

rail are two similar solenoids. The test coil and solenoids are rigidly 
connected together and mounted on a carriage which is free to 
travel along the test rail and its companion rail. Fig. 39 is a 
photograph of a pair of rails with the coils in place. Underneath 
the carriage is shown the electric motor which drives the apparatus 
along the length of the rails. 

Any change in the magnetic induction in the test rails manifests 
itself by a deflection of the galvanometer coil. The position of 
the galvanometer coil is recorded by means of a spot of light 
reflected onto a photographic film. In order to make a contin- 
uous record the film is driven at a uniform rate by an electric 
motor. The galvanometer and recording apparatus are shown 
in Fig. 40. A great many modifications of the method of ex- 
ploration were made. Some of the records, for example, were 
taken with one test coil surroimding each rail and coupled so 
that the emfs generated opposed each other. 

To explore the length of a rail the current in the magnetizing 
solenoid is adjusted and the electric motors driving the carriage 
and the film started simultaneously. 

In this preliminary work in order to get some idea of the im- 
portance of the magnetic irregularities observed several artifi- 
cial defects were made in some ordinary 100-pound rails which 
happened to be available. These rails had all been in service 
and had been submitted to the btueau because of suspected 
imperfections. In general, they are from the same heat as other 
rails which have caused wrecks or otherwise failed in service. 

In order to simulate the effect of a transverse fissure a saw 
slot I mm wide cutting away about 10 per cent of the section of 
the rail was made. This slot was filled in with high permea- 
bility transformer iron and the surface thus filled in was smoothed 
down with a file. 

Fig. 41 shows the magnetic effect of the saw slot very clearly. 
In a later test of this same saw slot without the soft iron filling 
the galvanometer deflection was so violent that the spot of light 
went far beyond the bounds of the film. In either case the 
magnetic test shows the position of the slot within i cm. On 
another rail a similar slot was cut into the base and gave a record 
of similar characteristics. 

To determine whether this method would detect a flaw in the 
web of a rail, records of the magnetic condition were made with 
holes drilled in the web. The effects of holes of various sizes are 



Bulletin Bureau of Standards, Vol. 13 





Fig. 39. — Photograph of rail-exploring apparatus 



i^^smtn 




Fig. 40. — Photograph of recording apparatus iised in the exploration of rails 



Burrmvs] Magnetic and Mechanical Properties of Steel 



205 



shown in Fig. 41. It is quite evident that such a defect does 
make itself known by the magnetic exploration, and that the 
magnetic importance is proportional to the size of the hole. 

In addition to the effects of the saw slot in the head and the 
holed drilled in the web, several other observations may be made 
on Fig. 40. The fact that the records are not all of the same 
length is due to slightly different rates of travel of the car in the 




-* /y 




Fig. 41. — Photographic record of inhomogeneities in a standard steel rail after service, 

showing the effect of artificial flaws 

various cases. The breaks in the curves are caused by shading 
the recording light beam at intervals corresponding to a carriage 
travel of 50 cm. The consistency with which the magnetic record 
repeats itself is quite evident from an examination. All the 
principal characteristics and most of the minor details of one 
curve are reproduced in the other two. The marked magnetic 
inhomogeneity noticed at the left of these records is due to some 



2o6 Bulletin of the Bureau of Standards [Voi. 13 

unknown characteristic of this region of the rail which, as yet, 
we have not had time to investigate. 

In Fig. 42 of another rail the record shows a wavy form of 
remarkable imiformity. It appears from a comparison of the 
magnetic record with the tie marks on the rail that there is a 
cycle of magnetic variation which repeats itself at distances 
equal to the spaces between ties. The portion of the rail over 
the tie is magnetically harder than the intermediate portions. 
This is of considerable interest because of the fact that rail failures 
occur more frequently over the ties than in the interspaces. The 
irregularity in the middle of the curve is worthy of comment. 
At the point A the cvuve shows a relative hardening instead of 
the maximum of magnetic softness that might be expected. 
The rail head was carefully examined in this region and was found 




Fig. 42. — Photographic record of a standard steel rail after service, showing the effect of 

tie strains and local hard spots 

to have imbedded in it a number of nodules of a metal of finer 
texture and greater hardness. It has been suggested that these 
may be small fragments from the rolls. 

Quite an ingenious application of the fact that mechanical 
inhomogeneities are accompanied by corresponding magnetic 
variations was made by McCann and Colson^^ in 1908. 

The apparatus consists essentially of a solenoid surrounding 
the mine hoist cable to be tested and connected in series with a 
suitable current source and measuring instrument. Any variation 
in the magnetic constants of the cable, due either to the breaking 
of individual strands or hardening caused by excessive strains, is 
indicated as soon as the defective portion passes through the 
apparatus. Suitable recording apparatus is provided so that a 
test of the entire cable is made every time the car travels the 
length of the shaft. 

' ' Western Electrician, 43, pp. 76-77; 1908. 



Btirrows] Magnetic and Mechanical Properties of Steel 207 

V. CONCLUSIONS 

The experimental evidence, of which only a small portion has 
been presented in this paper, seems to point to the conclusion 
that there is one and only one set of mechanical characteristics 
corresponding to a given set of magnetic characteristics, and con- 
versely there is one and only one set of magnetic characteristics 
corresponding to a given set of mechanical characteristics. 

Although there is no evidence to refute the preceding rather 
broad statement, the" utility of this generalization is decidedly 
limited by the complexity of the relations due to the large number 
of variables and the lack of sufficient quantitative data. Quan- 
titative data, however, are gradually being obtained by the author 
and others who are working on this problem. The application 
of the magnetic tests is further limited by practical difficulties in 
testing irregular shapes. Even with these limitations, magnetic 
testing in conjunction with mechanical testing may be expected 
to be of considerable value in determining mechanical properties. 

It has been shown that magnetic observations taken during the 
course of a tensile test indicate the time when the true elastic 
limit, the yield point, the necking down point, and the ultimate 
strength are reached. In addition, the magnetic data give some 
idea of the uniformity of the material. 

If it is once determined what treatment is requisite for a given 
steel, a magnetic test may be used to determine whether or not 
the material has been brought into the desired condition. 

It is quite possible that the magnetic data may be used to 
define a bar of steel. In no other manner than by a magnetic 
examination is it possible without doing violence to the specimens 
to determine whether two steel bars are identical in properties. 

A determination of the magnetic uniformity of a piece of steel 
may be used as an index of the mechanical homogeneity. 

A magnetic test indicates the character of the entire cross sec- 
tion of the metal, rather than merely a stuface phenomenon, as in 
the case of certain hardness tests. 

Notwithstanding the possibilities of the magnetic test, it must 
be remembered that at present they are possibilities only. Before 
the magnetic characteristics can be of much practical importance 
a great deal of investigation is necessary and a large number of 
accurate measurements on specimens of known chemical compo- 
sition and heat treatment must be made. 



2o8 Bulletin of the Bureau of Standards [Voi. 13 

Before a magnetic test can be of service as an indicator of the 
mechanical characteristics in any particular case, preliminary 
work must be done to determine the most suitable magnetic data 
and also the minimum amoimt which will give the desired informa- 
tion. Among the magnetic characteristics which may be used are 
permeability, residual induction, coercive force, hysteresis energy, 
etc., and each of these may be taken in connection with any one of 
a great number of magnetizing forces. 

For a concrete case, suppose that the problem is to devise a 
magnetic test for a steel spring or a crank axle. The preliminary 
investigation would take some such course as the following: 

1. Determination of magnetic normal induction curves and 
hysteresis data for test pieces made of the materials to be tested 
and submitted to the various heat and mechanical treatments that 
may be expected in practice. 

2. Comparison of the above magnetic data with the correspond- 
ing mechanical data and the determination of the most suitable 
magnetic data to use. 

3. Working out of the experimental details so that the required 
magnetic measurements may be made on the full-size commercial 
specimen. 

4. Checking out of magnetic and mechanical data on the full- 
size specimens to be sure that the same conditions are fulfilled as 
in the case of the original test pieces. 

Operations 1,2, and 4 are time consuming, but do not offer any 
great difficulties that can not be overcome by patient intelligent 
experimentation. The third operation may offer practical diffi- 
culties due to irregularities in the shape of the material to be 
tested. Relatively long objects uniform in diameter, such as rails, 
steel rims, band screws, drills, and steel cables, present no diffi- 
culty. Relatively long objects whose cross section changes 
gradually from section to section, such as spring leaves, straight 
axles, and files, present comparatively little difficulty. Relatively 
long objects of irregular section, such as crank axles, present great 
but not insuperable difficulty. Short, thick castings present 
difficulties which for the present seem insuperable. 

Washington, March 30, 1915. 



VI. BIBLIOGRAPHY 

The following is a list of references dealing with the correlation 
of the magnetic with other physical characteristics : 

1841. Joule. (Tension.) 

1847. Matteuci. Comp. Rend., 24, p. 301. (Tension.) 

1858-1886. Wiedemann. Pogg. Ann., 96, p. 17, 1858; 103, p. 566, 1858; 106, p. 161, 

1859; Wied. Ann., 27, p. 376, 1886; 41, p. 200, 1886. (Torsion.) 
1861. Righi. Beibl, 5, p. 62, 1881. (Hardness.) 
1863. von Waltenhofen. K. Akademie, 48, 1863. (Hardness.) 
1865. Villari. Pogg. Ann., 126, p. 87. (Tensicxn.) 

1874. Ruths. Inaug. Diss. -Darmstadt. (Hardness.) 

1875. Thompson. Proc. Roy. Soc. Lon., 23, pp. 445, 473. (Tension.) 

1875. von Waltenhofen. Dingler's Polj^ec. Jour., 217, pp. 357-360. (Hardness.) 

1876. Fromme. Gottingen Nachrichten, 1876. (Hardness.) 
1876. Ruths. Dortmtmd, 1876. (Hardness.) 

1876. Gaugain. Comp. Rend., 82, p. 144. (Hardness.) 

1876. Trfeve and Durassier. Comp. Rend., 82, p. 217. (Hardness.) 

1877. Thompson. Phil. Trans. Roy. Soc., 166, Pt. 2, p. 693. (Tension.) 

1878. Thompson. Proc. Roy. Soc. Lon., 27, p. 442. 
1878. Gray. Phil. Mag. (5), 6, p. 321. (Hardness.) 

1878. V. Kerpelz. (Chemistry — ^Hardness.) 

1879. Thompson. Phil. Trans.' Roy. Soc, 170, p. 55. (Tension.) 

1879. von Waltenhofen. Dingler's Polytech. Jovii., 232, pp. 141-J50. (Hardness.) 

1879. Thompson. Phil. Trans., 179, p. 55. (Torsion.) 

1879. Hughes. Proc. Roy. Soc. Lon., 32, pp. 25, 213. (Torsion.) 

1881. Pictet. Arch, de Gen. (3), 6, pp. 113-125. (Mag. hardness.) 

1881. Metcalf. Beibl., 5, p. 895. (Mag. hardness.) 

1883. Skida. Proc. Roy. Soc. Lon., 35, p. 404. (Tension.) 

1885. Eiving. Phil. Trans. Roy. Soc. (Tension.) 

1885. Barus and Strouhal. Bull. U. S. Geolog. Surv., 14. (Mag. hardness.) 

1888. Ewing. Phil. Trans. Roy. Soc. (Tension.) 

1889. Nagaoka. Phil. Mag., 27. (Torsion.) 

1890. Chree. Phil. Trans., 329, 1890. 

1891. Smith. Phil. Mag., 82, p. 383. (Torsion). 

1894. Squier. Electrician, 34, p. 90, 1894. (Magnetism of gun steel.) 

1896. Grosser. Diss. Rostock, 1896. (Torsional magnetostriction.) 

1896. Ebeling and Schmidt. Wied. Ann., 58, pp. 330-341. (Magnetic inhomo- 

geneity.) 
1900. Barus. Am. J. Sci., 10, p. 407. (Torsional magnetostriction.) 

1902. Lisell. Diss. Upsala, 1902. (Hydrostatic pressure.) 

1903. Fraichet. Eel. Elec, 36, pp. 361-369, 413-422. (Tension.) 

1904. Fraichet. Comp. Rend., 138, pp. 355-356. (Tension.) 
1904. Frisbie. Phys. Rev., 18, p. 432. (Hydrostatic pressure.) 

1904. Honda and Shimizu. Joum. Sci. Coll., Tokyo, 19. (Elasticity.) 
1904. Gerdien. Ann. de Phys., 14, p. 51. (Torsion.) 

1904. Bidwell. Roy. Soc. Proc, 74, p. 60. (Efiect of annealing on magnetostric- 
tion.) 

209 



2IO Bulletin of the Bureau of Standards [Voi.13 

igo6. Kaim. Phjrs. Zs., 1906, pp. 526-527. (Inhomogeneities.) 

1906. Piola and Tieri. Acad. Lin. Atti., 15, pp. 231, 566. (Torsion.) 

1907. Maurain. Jour, de Phys., 6, p. 380. (Torsion.) 

1907. Bouasse and Berthier. Ann. Chim. Phys., 10, pp. 199-228. (Torsion.) 
1907. Honda and Terada. Phil. Mag., 13, p. 36, 1907. (Elasticity.) 
1907. Honda and Terada. Phil. Mag., 14, p. 65, 1907. (Stress.) 

1907. Williams. Phil. Mag., 13, p. 635. (Hydrostatic pressure.) 

1908. Maurain. Jotu-. de Phy^., 7, p. 497. (Cyclic tension.) 

1908. McCann and Colson. Western Electric, 43, p. 76. (Inhomogeneities.) 
1908. Anonymous. Iron Age, 81, pp. 1162-1164. (Hardness.) 
1908. Wassmuth. Biebl, 32, p. 901. (Torsion.) 

1908. Gumlich and Vollhardt. E. T. Z., 88, pp. 903-907. (Influence of mechanical 
working.) 

1909. Brown. Roy. Dub. Soc. Pro., 17, pp. 101-175. (Mechanical influences.) 
1909. Brown. Roy. Dub. Soc. Pro., 12, pp. 101-122, 175-189. (Torsion.) 

1909. Burrows. Bull. Bureau of Standards, 6, pp. 59-62, 1909. (Inhomogeneities.) 
1909. Waggoner. Phy. Rev., 28, pp., 393-404. (Low temperature, carbon content.) 
1909. Mars. Stahl imd Eisen, 29, pp. 1673-1678, 1769-1781. (Hardness.) 

1909. Pellet. Jour, de Phys., 8, pp. 110-117. (Torsion.) 

1910. Du Prel. Diss. Mxinchen. (Hydrostatic presstu-e.) 

1910. Encoli. N. Cim., 20, pp. 317-340. (Tension and torsion.) 

1910. Brown. Roy. Dub. Soc. Proc, 12, pp. 36, 480-497. (Magnetotorsion, elastic 
limit.) 

191 1. Goerens. Iron and Steel Inst., Ill, pp. 320-400. (Effect of cold working and 
annealing.) 

1911. Ercoli. N. Cim. (6), 1, pp. 213-222, 237-268. (Tension and torsion.) 

1911. Brown. Roy. Dub. Soc. Proc., 12 (3), pp. 28-48. (Tension in nickel.) 

1912. Beckman. Arkiv for Mat. Astrofysik. (Hydrostatic pressure.) 

1912. Devries. Proc. I. A. T. M., Sixth Cong. (Tensile strength and hardness.) 
1912. Burrows. Proc. I. A. T. M., Sixth Cong. (Report on problem 28, general 
subject.) 

1912. Waggoner. Phy. Rev., 94, pp. 58-65. (Magnetic and elastic properties of a 
series of iron carbon allo3rs.) 

1913. Devries. Proc. A. S. T. M. (Hardness, toughness, tensile strength.) 

1913. Goerens. Stahl und Eisen, 34, pp. 282-285. (Magnetic and mechanical 

properties of mechanically hardened and annealed steel.) 
1913. BtUTOWs. Bull. Soc. Auto Engr., Nov., 1913. (General.) 

1913. Burrows. Proc. A. S. T. M. (Hardness, toughness, tensilestrength.) 

1914. Hadfield and Hopkinson. Lon. Eng., 97, pp. 756-759. (Magnetic and mechani- 
cal properties of manganese steel.) 

1914. Smith and Sherman. Phys. Rev. N. S., 4, pp. 267-273. (Tension and com- 
pression.) 

1914. Merica. Diss. Berlin. (Tension; many valuable data.) 

1914. Tafel. Stahl tmd Eisen, 34, pp. 574-578. (Tension.) (In drawn bars the 
B-H ciu-ve shows sharp changes near the yield point.) 

1914. Mathews. Proc. A. S. T. M., 14, pp. 50-71. (Hardness.) 
For a good bibliography on magnetostriction, see Dorsey, Phy. Rev., 30, p. 178, 

1910. 



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